The purpose of this work is to examine the chemical, biological and immunological properties of histocompatibility antigens (H-2) and tumor specific transplantation antigens (TSTA). The approach is to purify the molecules expressing these antigens and determine their properties at each stage of the purification. These properties include: 1) Ability to induce in vivo transplantation rejection and humoral response, 2) ability to stimulate lymphoid cells in vitro, 3) chemical properties with particular emphasis on how these molecules bind to biological membranes, 4) the metabolism of these antigens in normal and neoplastic cells. The rationale for this approach is that through purification of these antigens one can determine if there are any structural similarities which may explain their common biological activity, i.e., transplantation rejection. Furthermore, knowledge of the biological properties of these molecules will provide a rational basis for using them in in vivo therapeutic protocols. Finally, when they are purified, the chemical structure of these antigens will aid in the understanding of the organization of the genes which encode them.